1. Field of the Invention
The present invention relates to a method for preparing silver nanoparticles, and particularly to a method for preparing silver nanoparticles employing ethanolamine.
2. Related Prior Arts
So far, methods for producing silver nanoparticles are classified into physical methods and chemical methods. The physical method usually demands expensive equipment for highly-vacuum vaporization or e-beam. The chemical method uses reducers to reduce the silver ions to atoms and then a stabilizer is used to control the size of the particles. Representative reducers include NaBH4, formaldehyde, alcohol, hydrazine (H2N—NH2) and the like. Representative stabilizers include sodium citrate, glucose, sodium dodecyl sulfate, polyvinyl pyrrolidone (PVP), dendrimer, and the like.
To avoid aggregation and promote the stability of the silver nanoparticles, dispersants or protectors are usually added based on their static electricity or steric hindrance. The dispersants can be water soluble polymers, for example, polyvinylpyrrolidone (PVP), polyvinylalcohol (PVA), polymethylvinylether, poly(acrylic acid) (PAA), nonionic surfactants, chelating agents, etc.
Some stabilizers known in the art are disclosed in reports. In J. Phys. Chem. B 1998, 102, 10663-10666, sodium polyacrylateor polyacrylamide was provided as a stabilizer. In Chem. Mater. 2005, 17, 4630-4635, thioalkylated poly(ethylene glycol) was provided as a stabilizer. In J. Phys. Chem. B 1999, 103, 9533-9539, sodium citrate was provided as a stabilizer. In Langmuir 1996, 12, 3585-3589, nonionic surfactants were provided as stabilizers. In Langmuir 1997, 13, 1481-1485, NaBH4 was provided as a reducing agent and anionic, cationic, and nonionic surfactant were provided as stabilizers. In Langmuir 1999, 15, 948-951, 3-aminopropyltrimethoxysilane (APS) was provided as a stabilizer and N,N-dimethyl-formamide was used as a reducing agent.
As described above, the traditional method for stabilizing silver particles is to add surfactants or stabilizers. However, the solutions of such silver particles have solid contents less than 10% and have a higher solid content with aggregation.
Conventional chemical methods require the use of organic solvents, salts, or reducing agents for long-term and complex redox reactions, which result in high cost. Moreover, concentrations of the silver ions have to be lowered to ppm scale during operation or the silver particles will aggregate and perform undesired effects. Accordingly, there remains a need for developing more efficient and cost effective methods for preparing silver nanoparticles.